As the demand for integrated circuits having ever-smaller device features continues to increase, the need for improved illumination sources used for inspection of these ever-shrinking devices continues to grow. One such illumination source includes a laser-sustained plasma source. Laser-sustained plasma light sources are capable of producing high-power broadband light. Laser-sustained light sources operate by focusing laser radiation into a gas volume in order to excite the gas, such as argon or xenon, into a plasma state, which is capable of emitting light. This effect is typically referred to as “pumping” the plasma. Traditional plasma cells or lamps include plasma bulbs for containing gas used to generate plasma. Typically, plasma bulbs or lamps used in broadband wafer inspection tools are made of fused silica glass without the use of any additional surface coatings or layers. As a result, at the air-glass interface, Fresnel loss is observed resulting in a significant amount of lost pumping light and emitted broadband light.
As depicted in the conceptual view 10 of FIG. 1A, Fresnel loss results from a mismatch in refractive index at the air-glass interface, such as the interface 16 defined by the volume of air 12 and the surface of the glass 14. As shown in graph 20 of FIG. 1B, when light propagating through the air 12 impinges on the air-glass interface 16, the light begins to experience the refractive index of glass, which is higher than refractive index of air. As a result, a portion of the light is reflected back from the air-glass interface leading to a loss of light transmitted through the interface 16. In a typical air-glass interface, at normal incidence, approximately 4% of incident light power will be lost due to Fresnel loss.
In an effort to reduce this loss, some optics are coated with dielectric-based anti-reflection (AR) coatings, which are commonly formed using multiple layers of thin dielectric films. The temperatures in typical broadband lamps (e.g., plasma source, arc lamp and the like) used in broadband inspection tools are commonly operated at temperatures sufficient to cause significant degradation in the physical and/or optical properties of these dielectric coatings. As a result, typical dielectric AR coatings are not well-suited for use in high temperature environments such as plasma-based broadband light generation. Therefore, it would be desirable to provide an apparatus, system and/or method for curing defects such as those of the identified above.